Snapshot: layers.json bloat for service layers #50

Problem

A simple map with only two ArcGIS Online service layers produces a 100k+ line layers.json file on snapshot. This makes the export unnecessarily large and slow to parse.

Expected Behavior

layers.json should contain a concise summary of layer metadata — not the full service definition or all sublayer details. For service layers (map services, feature services, etc.), we should export only the essential properties needed for CLI queries.

Suggested Approach

• Identify which fields are being serialized that cause the bloat (likely full service metadata, renderer details, or field definitions)
• Filter exported properties to a relevant subset (name, URL, type, visibility, spatial reference, etc.)
• Consider a --full flag if users ever need the complete dump

Reproduction

1. Create a new map in ArcGIS Pro
2. Add two ArcGIS Online service layers
3. Run a snapshot export
4. Observe layers.json is 100k+ lines